Patients with Crohn's disease (CD) have a defective intestinal tight junction (TJ) barrier, manifested by an increase in intestinal paracellular permeability. The defective intestinal TJ barrier is an important pathogenic factor of CD that allows increased paracellular permeation of toxic luminal antigens, leading to intestinal inflammation. Interleukin-1( (IL-1(), a prototypical multi-functional pro-inflammatory cytokine, has been shown to play a central role in the intestinal inflammation process in the gastrointestinal tract. Recent studies indicate that an important pro-inflammatory action of IL-1( and other pro-inflammatory cytokines is to cause a functional opening of the intestinal TJ barrier, leading to an increase in paracellular permeability. The broad objectives of this grant application are to elucidate the cellular and molecular mechanisms that mediate the IL-1( induced increase in intestinal TJ permeability and to identify potential therapeutic targets to prevent the IL-1( induced increase in intestinal TJ permeability and subsequent development of intestinal inflammation, using an in-vitro (consisting of filter-grown Caco-2 intestinal epithelial monolayers) and a newly developed in-vivo mouse model system. Deciphering the intracellular pathways and the molecular mechanisms involved in IL-1( modulation of intestinal TJ barrier function has great potential scientific and clinical relevance in advancing novel scientific concepts regarding intestinal TJ barrier dysfunction during inflammation and for developing new therapeutic strategies that target the TJ barrier in preventing intestinal inflammation. Our preliminary studies suggested that the IL-1( induced increase in intestinal epithelial TJ permeability was mediated in part by: 1) activation of extracellular signal- regulated kinases 1 and 2 (ERK1/2) signaling cascade; 2) activation of myosin light chain kinase (MLCK) gene; and 3) microRNA (miRNA) induced degradation of occludin mRNA. Based on our preliminary data, we hypothesize that the IL-1( induced increase in intestinal TJ permeability is regulated in part by ERK1/2 signaling cascade induced activation of MLCK gene and subsequent increase in MLCK protein expression and by microRNA induced degradation of occludin mRNA and depletion of occludin protein. The proposed specific aims of this grant application are to: 1) delineate the intracellular signaling cascade and the molecular processes that mediate the IL-1( induced increase in intestinal TJ permeability; 2) delineate the cellular and molecular mechanisms that mediate the IL-1( induced down-regulation of occludin gene and protein expression; and 3) delineate the mechanisms that mediate the IL-1( induced increase in intestinal permeability in-vivo and the therapeutic implications of preservation of intestinal TJ barrier function in-vivo. PUBLIC HEALTH RELEVANCE: Patients with Crohn's disease have a leaky gut, characterized by an increase in intestinal permeability to harmful antigens in the intestinal lumen. The studies proposed in this grant application seek to determine the intracellular and molecular processes that contribute to the leaky gut of Crohn's disease. Interleukin-1( has been shown to play an important role in promoting intestinal inflammation in Crohn's disease and other inflammatory conditions of the gut. The focus of these studies will be to delineate the intracellular and molecular processes that mediate the interleukin-1( induced disturbance of intestinal barrier function. The proposed studies also seek to identify potential therapeutic targets and strategies to induce therapeutic re-tightening or normalization of leaky gut in Crohn's disease.